An interline agreement is a basic treaty between airlines to handle passengers traveling on itineraries that require multiple flights on different carriers, allowing for single ticketing and baggage check-through.
What Is an Interline Agreement?
An interline agreement is a formal contract between two or more airlines that allows passengers to travel on a single ticket across multiple carriers, with baggage checked through to the final destination. It enables airlines that do not otherwise partner in an alliance or codeshare to still sell connecting itineraries and handle passenger rebooking, delays, and baggage transfers cooperatively. Interline agreements have existed since the early decades of commercial aviation, predating modern alliances like Star Alliance and SkyTeam, and remain the foundational legal framework that makes multi-carrier travel possible. Without one, passengers would need separate tickets for each flight segment, with no guaranteed protection if a connection is missed.
How It Works
Under an interline agreement, one airline can issue a ticket covering flights operated by another carrier, using standardized IATA ticketing and settlement systems to divide revenue between the airlines involved. Baggage is checked once at the origin airport and transferred automatically at connecting airports, even when carriers use different terminals. If a delay or cancellation on one carrier causes a missed connection, the receiving airline is typically obligated to rebook the passenger on its next available flight, sometimes at no extra charge, depending on the agreement's specific terms. These agreements are narrower than codeshares, which involve shared flight numbers and joint marketing.
Where Interline Agreements Apply
Interline agreements are common between full-service carriers, regional airlines, and even airlines outside formal alliances, allowing broader route coverage than any single carrier's network provides. Legacy carriers such as those in Star Alliance, SkyTeam, and Oneworld maintain interline deals with non-alliance airlines to extend reach into markets they don't directly serve. Low-cost carriers historically avoided interline agreements to keep operations simple and costs low, though some have begun adopting limited interline arrangements for select long-haul or international connections in recent years.
Traveler Tip
Before booking a multi-airline itinerary, confirm whether the carriers have an interline agreement — this determines whether your bags transfer automatically and whether you're protected if you misconnect. Self-connecting on separate tickets without an interline agreement carries real risk if delays occur. CEOFLIGHTS specialists can help find discounted fares — call (888) 851-6897.
